....
Of course, the case of the 50-move rule (or similar) is similar. It can reveal when a player has faffed around to waste time to reach a position (all the time in the same tablebase - i.e. specific material), reaching a position which would be a win if he had enough moves but which is not without.
In this situation, the tablebase will tell us that the mate that would be available isn't because the 50 move rule scuppers it, but does it tell us when (and how) a player might still have a win by finding a different route, necessarily one that zeros the 50 move counter?
In an hypothetical variant of chess that implements the 50 move rule but not a repetition rule (which is what the Syzygy table assumes) then if Syzygy tells you it's scuppered under the 50 move rule it is. Syzygy effectively assumes worst case which is why it plays such weird mates as I posted here.
Positions with the type of alternate route you refer to are already taken into account and classed as wins. Syzygy plays the most inclusive alternate routes.
It could still be scuppered in competition rules chess without it telling you, which is what the KRK position under discussion was about.
As well as the question at the end of my edited post above, consider the odd case where one player is table-base assisted and has to take advantage of the other player having given up the win by faffing around and becoming blocked from the win as a result.
Do tablebases contain enough information to enable this assisted player to force the draw? There is only a question about play that takes place before the next irreversible move - after that point normal use of the tablebase becomes optimal again.
I think the answer is no. I think there may be cases where that could be achieved but only with moves not all recommended in the Syzygy tablebase. I'll try and think of one.
Of course Syzygy effectively contains all winning positions, so if you constructed a piggy back tablebase that avoided all repeated basic rules positions in the position you describe selecting only un Syzygy winning moves, it would be quicker than considering all un legal moves. So you might consider that containing enough information. You then make only drawing moves in the resulting piggy back tablebase (which would of course be valid only for that particular position).